Steel alloy



G. v. LUERssEN ET Al. 2,355,224

STEEL ALLOY Filed April 29, 1942 5 Sheets-Sheet l Aug. 8, 1944.

G. v. LUERSSEN ET AL STEEL ALLOY 5 sneet-sheet 2 Filgd April 29. 1942 INVENTORS foxef V-'aE/SEN BY CARL B. Pos-r Arme/v525 G. V. LUERSSEN ET AL Aug. 8, 1944.

STEEL ALLOY 5 Sheets-Sheet 3 Filed April 29, 1942 IN1/mrow eff Vf/wsc/v BY CARL, B. Paar w Arron/Z525 Aug 8, 1944. G. v. LUERSSEN ET A1. 2,355,224

STEEL ALLOY Filed April 29, 1942 5 Sheets-Sheet 4 'mvENToRs G50/ess M afessen RL p0 7".

ATTORNEYS Aug 8, 1944. G.' v. LUERssEN ET Al. 2,355,224

STEEL ALLOY Filed April 29, 1942 l 5 Sheets-Sheet 5 INVENToRs GEORGE K UE/Qssfw ATTORNEYS Patented Aug. 8, 1944 rl'JlJfi'ri-:D srArEs PATENT OFFICE Pa., ass

ignors to The Carpenter Steel Company, l

` Reading, Pa., a corporation of New Jersey Application April 29, 1942, Serial No. 441,018 4 Claims. (Cl. 'l5-126) This invention relates to an improvement in air-hardening steels of that class which contains manganese, chromium,` and ,molybdenum.' An object of this invention is to improve this kind of steel alloy so that large sections may be air hardened throughout from a relatively-low heat treating temperature. It is also an object to reduce the amount of alloying'material .which it is necessary to use and yet-` obtain the advantageous results for which this alloying material has been used in the past. v

With ordinary carbon steels, it is necessary to I cool rapidly from a heat-treating temperature through the critical temperature range in order.

to producey certain hardening `characteristics. This so,ca1led cooling or quenching," when carried out rapidly, brings with it some grave disadvantages, such as the setting up of undesirable internal stresses, cracks, distortions, and the like. In order to avoid these difculties, certain elements, such as manganese, chromium, and molybf Molybde- Air treating Carbon.- Manganese Chromium num i temperature Percentl lPerce'n'i Percenty Percent F.

These steels, however, cannot be air hardened to a Rockwell hardness of C59 orfmore in sections larger than 2" -round x 3 or 4" long, unless temperatures in the neighborhood of 1700/1800 F. are used. Sections 4" round x 4" long of these steels must be air treated from temperatures in the neighborhood of l700/1800 F.,in order to obtain a Rockwell hardness of C-59 or greater throughout the section.

In order to obtain air-hardening properties in d sections approximately 6" round x 6" long, the

prior metallurgical art; has resorted to increased chromium contents, which in turn lead to higher heat treating temperatures. This is illustrated by the following analysis which shows a steel With the analyses as known to the prior art, however, resort must be had to high treating temperatures in order to harden sections larger than 4" round x 4" long. When any steelis hardened from high temperatures two serious defects arise; (1) the steel is subject to severe scaling on the surface which leads to decarburization, and (2), grain growth is encountered if the steel is allowed to go slightly over its normal treating temperature. The first defect, generally leads to extra grinding and preparation costs in the fabrication of dies, etc., while the second will lead to "brittle" dies and tools as compared to those steels which are une grained after heat treatment.

The following examples are given to illustrate which will air-harden in sections approximately 6" round x 6" long from the temperatures indicated:

` Steel of this analysis will not harden from any the limitations of the prior vart air hardening Carbon Manganese Chromium Molybdenum Percent Percent Percent` Percent 1.00 2.00 75 75 However, in sections larger than 1" round x`2 feasible tool treating temperature to a Rockwell hardness of C-59 or greater in sections larger than 6" round x 6" long.

We have discovered that by lowering the carbon content from the accepted 1% in these manganese-chromium-molybdenum steels, there is' a marked increase in hardness penetration in sizes of sections ranging from 1" square to 10" round x 10" long and that if the alloying constituents are properly proportioned, such penetration can be obtained by hardening from relatively low temperatures, not exceeding 1600 F., with a saving of alloying content and with an advantageous fractured grain size.

The prior metallurgical art has recognized certain advantages to be associated with grain size of steel as displayed by the fracture appearance.

scale numbered l to with the grain becoming nner as the fracture number increases. A set of fractures comprising ten steps representing these gradations fromfcoarse to fine grained steels is commonly known as Shepherd standard fractures." In the case of tool steels it is highly desirable to manufacture a steel with the iinest grain size possible when treated from the normal hardening temperature of the steel. A line grained fracture is generally one which corresponds to the Shepherd classincation of 8 to 10, while a fracture number of '7 or less is generally classed as a coarse grain size.

We have found that, in an alloy containing 2.00% manganese, 1.00% chromium, and 1.00% molybdenum, if the carbon content is kept down between .60% and .80%, a 4" round x 4" long section can be air-treated from a temperature of 15251550 F. to yield an inside Rockwell hardness of C-59 or greater, while a section of the same size treated at the same heat treating temperature but with 1.00% carbon, has an inside Rockwell of only about C-50.

In this alloy containing 2.00% manganese,

' 1.00% chromium and 1.00% molybdenum, if the carbon content is kept between .70% and .80%, a section 6" round x 6" long can be air treated from a temperature of 1575 F. to yield an inside Rockwell hardness of C63/64, while a section of the same size, treated at the same heat treating temperature, but with .96% carbon would have an inside Rockwell hardness of only C5i .l We have also found that in an alloy containing 3.00% manganese, 2.50% chromium and 2.50% molybdenum, if the carbon content is kept between .60% and .80%, a section 10" round x 10" long can be air treated from a temperature 'of 1u50/l600 F. to yield an inside Rockwell hardness of C-63, while a section of the same size, treated at the same heat treating temperature, but with 1.00% carbon had an inside Rockwell hardness of only C57.

These tests indicate that an alloy containing approximately .60% to .80% carbon, 2.00%/3.00% manganese, 1.00%/2.50% chromium and 100%/ 2.50% molybdenum can be air treated in sections larger than 6" round x 6" long at temperatures of 1550/1600 F. to yield inside Rockwell hardnesses of C-59 or greater, whereas the same alloys and same sections with 1.00% carbon must be air treated from temperatures of approximately 1800 F. `to yield an inside Rockwell hardness of C-59 or greater. However, it can be demonstrated that grain coarsening will be encountered in the alloys containing 1.00% carbon when air treatingtemperatures of approximately 1800 F. are used, and this makes the use of these high air treating temperatures very undesirable.

As a general rule it can be said that the higher the alloy content of steel the slower will be its critical cooling velocity, i. e., the rate at which it must be cooled past its critical temperature range in order to obtain a completely hardened structure. Thus, if hardness penetration in large rounds were the only property desired in an alloy steel, it would sulce merely to increase the alloy content. If the total alloy content were increased .in this manner, probably any desired depth of penetration could be obtained in any size section, but this higher alloy content would immediately necessitate air treating from much higher treating temperatures, or would increase quite markedly the annealing diilicuities. Either of these results would be detrimental, because it would be necessary that the steel be annealed soft Y emphasize the necessity for balancing the alloy content of deep air-hardening steels in such a manner that the alloy can be' annealed without diillculty and also be capable of air-hardening in these large sections from low treating temperatures.

`Using manganese chromium molybdenum steels with a carbon content of approximately .70%, we have determined the necessary proportions of manganese, chromium, and molybdenum to give an air hardening steel capable of being air treated from a temperature of not more than 1600 F. to yield an inside Rockwell hardness of (L-(SO or more at the center of large sections, i. e., sections 4" round x 4" long or larger. In order to do this, we have made a number of specimens with carbon contents nearly constant at .A70-.75% with the manganese content ranging from'.50 3.00%, chromium nil to 5.00%, and molybdenum from nil to 5.00%.' A melting series was devised so that various proportions of manganese, chromium, and molybdenum would coexist with one another in the different specimens. The various specimens were air-treated from 1500 F. to 1900 F. in steps of 100 F. After air cooling to room temperature, Rockwell hardnesses were obtained on freshly ground surfaces of the specimens and those which air-hardened were subsequentlyfractured and inside Rockwell hardnesses obtained.

The figures of the appended drawings show graphically the eiect in a .G0-.80% carbon steel of lvarying proportions of manganese, chromium,

and molybdenum on the air-hardening properties.

Fig. 1 is a pseudo-ternary diagram of .60%- .80% carbon steels with a total alloy content of 30G-4.00%', when air-hardened from 1500 F. The diagram shows a stippled area wherein the fracture grain size is at least 8% and an area both stippled and cross-hatched wherein it is less than 8%. The Rockwell hardness is indicated by the figures in circles, and the position of each circle shows the proportions of alloying constituents for the indicated Rockwell hardness.

Figs. 2, 3, and 4 are similar to Fig. 1 but for hardening temperatures from 1600" F., 1700 F., and 1900 F., respectively.

Figs. 5, 6, '1, and 8 are similar to Figs. 1, 2, 3, and 4, except that these diagrams are for .6D-.80% carbon steels having a total alloy contentv of 5mi-6.00%.

Figs. 9, 10, 1l, and 12 are similar to Figs. 1. 2. 3, and 4, except that these diagrams are for .6D-% carbon steels having a total alloy content of 'LOD-8.00%.

Fig. 13 is a three-dimensional diagram showing the relationship between manganese, chromium, and molybdenum, and the total alloy con- For example, if the alloy being considered is composed of 2.00% Mn, 2.00% Cr, land 1.00%

Mo, then the relative proportions of manganese, chromium, and molybdenum 1n this alloy containing a 5.00% total alloy are 40%, 40%, and 20%, respectively.. For an alloy containing 3.00% Mn, 4.00% Cr, and 3.00% Mo, the relative proportions of manganese, chromium, and molybdenum in this total alloy content analysis is considered to be 30%, 40%, and 30%, respecspectively. Using this system of presentation of inside Rockwell hardnesses obtained at various air-treating'temperatures for these .various alloys, the relative proportions of. manganesetween the alloying elements, manganese, chrochromium, and molybdenum is represented in these ternary diagrams whose vertical axes represent the total alloy content in percent by weight.

The circles shown inside the ternary diagrams indicate the relative proportions of manganese, chromium, and molybdenum by weight, and the iigures inside the circles refer to the Rockwell C hardnesses obtained at the air-treating temperatures referred to for each ligure.

The stippled areas representan-hardening al. loys of a Rockwell hardness in excess of C-59 and a fracture vgrain size of at least 83/4. The

areas which are both stlppled and cross-hatched represent air-hardening alloys of a lRockwell hardness in excess of C59 but a grain size of general conclusions can be drawn in regard to desirable proportions of the alloyins elements in lmanganese-chromium-molybdenuml steels havingabout.'10% carbon:

In a steel with a total alloy content by weight ct 2.50%. the manganese should be equal to or greater than nine times the chromium content We claim: 1. A deep air hardening steel capable of being air hardened in sections at least as large as those l0 for commercial machining requirements, said steel having a carbon content of about 0.60 to 0.80 per cent., a total alloy content of about 3 to about 8 per cent. and the balance principally iron, and in which steel the relationship bemium, and molybdenum and the total alloy content is that deiined by the volume A, B, C, D, delineated in Figs. 13 and 14, and the areas A2, B2, C, A, B6, C, and A1, B1, C1o of Figs. 2', 6,

and 10, respectively) 2. A deep air hardening steel capableof being air hardened in sections at least as large as those typied by sections 4 inches round x 4 inches long, from temperatures no higher than about 1600 degrees Fahrenheit, to give a. Rockwell C (Re) hardness of at least about 60 and a fracture grain size of at least about 8, and' capable of being annealed to a condition sumciently soft for commercial machining requirements, said steel having a carbon content of about 0.60 to 0.80 per cent..

a total alloy content of about 3 to 4 per cent. and the balance principally iron, and in which steel the relationship between the alloying elements, manganese, chromium, and molybdenum is that dened by the area A2, B2, C2 of Fig. 2.

3. A deep air hardening steel capable of being air hardened in sections at least as large as those long, from temperatures no higher than about u 1600 degrees Fahrenheit, to give a Rockwell C (Ro) hardness ofat least about and a fracture grain size of at least about 8, and capable of beingv annealed to a condition sumciently soft for commercial machining requirements, said steel and equal to or crestor thanthe molybdenum conu having a carbon content or about 0.60 to 0.80 per tent.

In a steel having a total alloy content by weight ci 3.00-4.00%, the manganese should be equal to or greater than the chromium content and equal cent.. a total alloy content ot about 5 to 6 per cent. `and the balance principally iron, and in which steel the relationship between the alloyins elements. manganese. chromium, and molybto or mater umn one-third or the molybdenum o annum u that donned bv the area A. B', co or content.l j

In a steel with a total alloy .content by weight of 1h00-6.00%, the manganese should be `etmal toorsresterthantwo-thirdsotthechromium of the mobbdenum content.

In a steel having a total alloy content by weisht oi' 'M0-8.00%. the manganese should be equal to or greater than one-third of the chromium con- 4. A deep air'hardenlng steel capable of-beins air hardened in sections at least as large as those typified by sections 4 inches round x 4 inches lons.

'content and equal to or greater than one-third u from temperatures no higher than about 1600 desrecs Fahrenheit. to sive anockwell C (Re) hardness ci at least about and a fracture srain 'sise c! at least about 8, and capable of being annealed to a condition sumclently soit for tent and equal to or greater than one-fourth of n commercial machining requirements, said steel themolybdenum content.

In a steel having a total alloy content by weight of 10.00%, the manganese should be equal to or sreater than one-third of the chromium content having a carbon content ci about 0.80 to 0.80 per cent.. a total alloying content of about 7 to about 8 per cent. and the balance principally iron, and in which steel the relationship between the alloylnd equal t0 or sreater than one-mth o! the ing elements, manganese, chromium, and molybcontent. While `we have shown the invention as emdenm u that donned by tno ons A, n, c1

` GEORGE `V. LUERSSEN.

CARL B. POST.

ircmthescopecitheinvention n withnutdepirtinl ldmbythlmdedcm 

